The terrestrial digital broadcasting that has started broadcasting recently employs orthogonal frequency division multiplexing (called OFDM from now on). It uses many carrier waves passing through multivalued digital modulation such as 64-valued quadrature amplitude modulation to carry out large volume data transmission such as Hi-Vision video transmission within a limited broadcasting frequency bandwidth.
To carry out mobile reception of the broadcasting based on this transmission scheme with a vehicle-mounted receiver or the like, it is known that a single receiving system can hardly achieve sufficient receiving quality by circumventing the adverse effect of the fading and the like. Accordingly, a diversity digital broadcast receiving apparatus having two or more receiving systems is employed as will be described below.
The conventional digital broadcast receiving apparatus has two sets of antennas, receiving demodulation sections and synthesizers and a decoding section and a control section. The conventional digital broadcast receiving apparatus causes the two synthesizers to output the same selection frequency signals at the normal communication; supplies the decoding section with the demodulation output from the receiving demodulation section having greater receiving field strength information between the two receiving demodulation sections; and causes, during vacant channel search or channel switching, one of the synthesizers to output the selection frequency signal of that channel in communication, and the other one of the synthesizers to output the selection frequency signal of the destination channel of the channel switching (see Patent Document 1, for example). In addition, when the first receiving apparatus that receives a terrestrial digital television broadcasting wave is started by user operation, the second receiving apparatus that receives a terrestrial digital radio broadcasting wave carries out the channel search and information separation. Thus, while the first receiving apparatus offers a television program to a user, the second receiving apparatus acquires information for receiving broadcasts to cope with changes in receiving areas. There is another system that switches, when the user instructs to switch in accordance with the area through a remote control transmitter or the like, the receiving frequency of the tuner of the first receiving apparatus in response to the broadcast receiving information about the area acquired by a CPU (see Patent Document 2, for example).
Patent Document 1: Japanese patent application laid-open No. 9-36843/1997.
Patent Document 2: Japanese patent application laid-open No. 2004-64590.
With the foregoing configuration, the conventional digital broadcast receiving apparatus carries out the reception based on the combined diversity with the two receiving systems to obtain high receiving quality in the mobile reception.
On the other hand, the digital broadcasting can provide a user with conveniences by transmitting broadcast-related data in addition to the audio-video signal. More specifically, it provides program information to notify the user of future broadcasting contents. However, since the terrestrial wave digital broadcasting does not transmit information about the other broadcasting stations, although the user can obtain information about the receiving station, he or she cannot acquire information about the other stations not being received.
In view of this, a home-use digital broadcasting receiver activates its receiving circuit only when a user does not view without offering any audio-video information, and collects and stores receivable broadcasting information successively for future use as necessary.
As for the vehicle-mounted receiver, however, there is no guarantee that the power is supplied to the receiver while the user is not viewing or listening. Normally, when the user leaves a car, the power, which is usually supplied from an accessory power supply of the car, is turned off. Thus, it is rather rare that the power is supplied to the receiving apparatus while the user is not viewing or listening. Accordingly, there is a problem of being unable to correct the receivable broadcasting information while the user is not viewing or listening.
The present invention is implemented to solve the foregoing problems. Therefore it is an object of the present invention to provide a digital broadcast receiving apparatus having functions of not only maintaining stable receiving performance during moving by the diversity receiving function with two receiving systems by making effective use of the two receiving systems, but also receiving the broadcasting signal from a station to be viewed with a first receiving system, and receiving broadcasting waves of other stations with a second receiving system to acquire program-related information about the other stations.